1. Field of the Invention
The present invention relates to a method for producing hollow silica particles, and more particularly to a method of utilizing the amine-ketimine compound as a core template for producing hollow silica particles. In addition, the present invention also relates to hollow silica particles produced by the afore-mentioned method.
2. Description of the Prior Arts
Hollow silica particles, e.g. silicon dioxide particles with hollow structure, can be applied in a quite wide range of applications such as catalysts, absorbents, gas storage, capsule material, material with low dielectric constant, and various hollow tube materials. Besides, the hollow silica particles can be further applied in a medical related filed due to their properties of large specific surface area, high mechanical stability, low toxicity, and high biocompatibility.
Recently, processes for producing particles with hollow structure can be classified into template method, liquid-phase method, vapor-phase method, and arc discharge method. Wherein, the template method relates to a synthesis method that can effectively control the morphology of particles, and it is further divided into hard template and soft template approaches depending on the characteristics of the template. By choosing various templates, compounds formed in various structures can be produced by the template methods.
For hard template method, resin balls or solid metal compounds, such as polystyrene (PS), polymethyl(meth)acrylate (PMMA) and hematite, are usually used as the core template. Silica shells are formed onto the core template by chemical vapor deposition or high-temperature pyrolysis. After removing core template by acid etching or calcination, the hollow silica particles are finally produced. For soft template method, a liquid or gas, such as alkanes or primary amines having carbon numbers from 6 to 18, segmented poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) (PEG-PPG-PEG, F127), are usually used as the core template to produce hollow silica particles.
Generally, a hydrophobic material is usually used as the core template. Siloxane precursor for forming silica shells becomes a negative charge medium after its hydrolysis. In order to improving the affinity between the core template and silocane precursor, the surface of hydrophobic core template is modified with polycations or cationic surfactant to become positive-charged, or absorbs a coupling reagent, poly(vinyl pyrrolidone). Therefore, the hydrolyzed siloxane precursor can be adsorbed onto the surface of the modified hydrophobic core template. Subsequently, the organic siloxane compounds will be subjected to a co-condensation reaction on micelle surfaces, and then the produced silicon dioxides are deposited onto the micelle surface and formed a core-shell structure. After high-temperature sintering or acid etching, a shell-shaped ball having hollow structure will finally be produced.
Hence, according to the conventional method for producing hollow silica particles, there is a need to add surfactants and acid or basic solution to form the hollow silica particles.